Heat Exposure Safety and Risk Factors

Summer is here and being outside in the heat can take a toll on your body if you’re not properly prepared. It’s important to regulate your body temperature by both hydrating and gradually acclimating your body to withstand the increasingly hot conditions. Your body has “heat control mechanisms” which get overworked in hot, humid and poorly ventilated areas. When you’re exercising or doing physical labor, your muscles generate heat as a metabolic by-product.

 

Sweating can dissipate heat when the air is dry or a breeze is blowing. But when humidity rises and the air becomes denser, sweat doesn’t evaporate from the skin as readily. When this occurs, your core body temperature becomes too high and you can suffer from heat cramps, heat exhaustion or heat stroke. This heat stress can occur suddenly and be very dangerous, that’s why it’s important to be able to recognize the warning signals. This chart will help you identify your body’s heat stress signals and apply the appropriate action to prevent heat-related problems.

Margie Snyder, assistant director of solutions at The Hartford, recommends that businesses provide employees with spaces to combat heat exposure. “In addition to delivering first-aid treatment and injury prevention solutions, staffing an on-site clinician can also help keep employees healthy and safe at work,” said Snyder. “Having a resource for safety awareness and proactively ensuring staff are kept hydrated and cool can go a long way to reduce risk of injury. Having an extra set of eyes to identify the first signs of dehydration and heat-related concerns could potentially be the difference between a minor incident and a serious heat related illness.”

 

Workers exposed to hot indoor environments or hot and humid conditions outdoors are at risk of heat-related illnesses, especially those doing heavy work tasks or using bulky or non-breathable protective clothing and equipment. Workers at risk of heat stress include outdoor workers and workers in hot environments, such as firefighters, bakery workers, farmers, construction workers, miners, boiler room workers, factory workers and others. Some workers might be at greater risk than others if they have not built up a tolerance to hot conditions or have certain health conditions. Workers at greater risk of heat stress include those who are 65 years or older, are overweight, have heart disease, high blood pressure or take medications that may be affected by extreme heat.

 

Here is a breakdown of the top seven heat disorder factors which may impact an individual’s risk in relation to heat exposure:

 

The aging process results in a more sluggish response of the sweat glands, which leads to a less effective control of body temperature in the sedentary individual. Aging also results in a decreased level of skin blood flow associated with exposure to heat. The cause remains undetermined, but the decrease in skin blood flow implies an impaired thermoregulatory mechanism, possibly related to reduced efficiency of the sympathetic nervous system. For women, it has been found that the skin temperature increases with age in moderate and high heat loads, but not in low heat loads. Chronic hypohydration increases with age, which may be a factor in the observed higher incidence of fatal and nonfatal heat stroke in older study groups. The reasons for hypohydration in older adults appear to be related to a decreased thirst drive resulting in, among other things, a suboptimal plasma volume. A reduced plasma volume (and most likely total body water, given the normal transfer of fluids between compartments) can impair thermoregulatory dynamics. Another study suggests that age-related impairments in heat loss may not be evident during durations of less than 15 minutes of exercise; therefore, older workers may be safe from thermal strain and dehydration if they work for shorter intervals.

 

Older people are more susceptible to the effects of heat, and a significant fraction of those who suffer from heat disorders are older than 60. Age-related susceptibility to heat is multifactorial and may be related to decreases in sweating and cutaneous blood flow, changes in cardiovascular function and decreases in overall fitness. Decreased sweating may be due to reduced sweat production rather than a reduced number of sweat glands. So while acclimatization to heat can occur in the elderly, the rate of acclimatization is reduced.

 

Although not all aspects of heat tolerance in women have been fully examined, their thermoregulatory capacities have been. An average-sized woman has a lower aerobic capacity than an average-sized man. When they work at similar proportions of their maximum oxygen consumption, women perform either similarly or only slightly less well than men. According to one study, there seemed to be little change in thermoregulatory capacities at different times during women’s menstrual cycles.

 

Pregnancy is a consideration for women in coping with heat stress and as it progresses, tolerance of heat stress is reduced. Pregnancy naturally elevates the body’s temperature, subjecting women to heat exhaustion more rapidly during periods of extreme temperatures. The fetus acts as a source of metabolic heat and increases the weight of the mother. Also, because the pregnant woman is caring for more than one body, more fluids and energy are needed to cool her core temperature. One researcher reported that increased heat loads during early pregnancy raise the fetus’ risk of teratogenic effects. However, earlier studies suggested that the basal core temperature of pregnant women participating in submaximal exercise (i.e., bicycle test) studies over the course of their pregnancy decreased slightly postpartum. This result agrees with an even earlier study, reporting that the magnitude of any first trimester exercise-associated thermal stress for the embryo or fetus is reduced by the maternal physiologic adaptions during pregnancy. Moderate thermal stress (21.1°C [70°F] for 20 minutes) did not induce regular uterine contractility, nor was it harmful to the fetus when it was exposed during late pregnancy.

 

Obesity predisposes individuals to heat disorders. In fact, heat disorders occur 3.5 times more frequently in the obese than in lean individuals. The ratio of body surface area to body weight in the obese individual becomes less favorable for heat dissipation. Probably more important is the lower physical fitness and decreased maximum work capacity and cardiovascular capacity frequently associated with obesity. The increased layer of subcutaneous fat provides an insulation barrier between the skin and the deep-lying tissues. The fat layer theoretically reduces the direct transfer of heat from the muscles to the skin.

 

The extra weight carried by obese individuals results in an increase in metabolic energy for any given task. The increase in metabolic energy produced in the form of muscular work results in an increase in body temperature that must be exchanged, in comparison with a lean individual performing the same task in the same environment. Therefore, because it is apparent that obesity places the individual at a significantly higher risk of suffering a heat-related illness at any given workload or environmental temperature than the risk for a lean individual, additional accommodations may be necessary.

 

It is hard to separate drugs used therapeutically from those used socially. Alcohol use (combined with heat stress) commonly has been associated with the occurrence of heat stroke. It is a drug which interferes with central and peripheral nervous function and is associated with dehydration by suppressing Antidiuretic Hormone (ADH) production. The ingestion of alcohol prior to or during work in the heat should not be permitted because it reduces heat tolerance and increases the risk of heat-related illnesses.

 

There are many drugs other than alcohol that are used on social occasions and have played a part in cases of heat disorder, sometimes leading to death. Caffeine may be considered a socially accepted drug found in common beverages and foods (e.g., coffee, tea, soft drinks, energy drinks, cocoa, chocolate). It’s also used in some over-the-counter analgesics that are consumed worldwide to enhance alertness, reduce fatigue, enhance athletic performance and augment the effects of mild analgesics. Coffee is one of the most widely consumed beverages in the world and contains caffeine, which has a mild diuretic effect and should not be provided to workers to replace fluids lost to sweating. Moreover, coffee is generally consumed as a hot beverage and has the potential to exacerbate heat stress. Water is the preferred hydrating beverage for before, during and after work.

 

Caffeine-containing fluids are now marketed to the public as energy drinks. These drinks contain higher than normal doses of caffeine (more than what is found in a cup of coffee or soft drink) and have been used extensively among competitive athletes prior to participation in athletic events. The lethal oral dose for caffeine in humans has been reported to range between 18 and 50 grams. Other than the diuretic effects, this dose of caffeine is capable of inducing cardiac arrhythmias, which could be heightened by heat stress (i.e., as a result of already existing cardiovascular strain). It seems that there would also be a tendency to drink several energy drinks just to alleviate thirst as they are often available in smaller containers with less liquid, thus inadvertently overdosing on caffeine.

 

Many drugs prescribed for therapeutic purposes can interfere with thermoregulation. Some of these drugs are anticholinergic in nature or involve inhibition of monoamine oxidative reactions, but almost any drug that affects the central nervous system’s activity, cardiovascular reserve (e.g., beta blockers) or body hydration could potentially affect heat tolerance. Cardioselective beta blockers (e.g., atenolol, betaxolol, metoprolol and acebutolol) do not allow the small blood vessels in the skin to dilate, thereby reducing blood flow, which impedes sweat production and causes body temperature to rise. Thus, beta blockers predispose those working in heat to heat-related emergencies. A worker who requires therapeutic medications should be under the supervision of a responsible health care provider who understands the potential ramifications of drugs on heat tolerance. In such instances, a worker taking therapeutic medications who is exposed only intermittently or occasionally to a hot environment should seek the guidance from the responsible health care provider.

 

Individuals suffering from degenerative diseases of the cardiovascular system and other diseases, such as diabetes or simple malnutrition, are at increased risk when they are exposed to heat and when stress is imposed on the cardiovascular system. This outcome is readily seen during sudden or prolonged heat waves in urban areas where there is a sudden increase in mortality. This tends to more greatly affect older individuals who have age-related reduced physiologic reserves. In prolonged heat waves, the mortality is higher in the early phase of the heat wave. While acclimatization may play a part in the decrease in mortality during the latter part of a prolonged heat wave, the increased death rate in the early days of a heat wave may reflect an “accelerated mortality,” with the most vulnerable more likely to succumb at that time rather than more gradually as a result of degenerative diseases.

 

Any sicknesses or diseases in which gastrointestinal (GI) permeability is compromised could result in greater susceptibility to leakage of endotoxin and the cascade of immune reactions and death that occur with heat stroke.

 

In all experimental studies of the responses of humans to hot environmental conditions, a wide variation in responses has been observed. These variations are seen not only between individuals, but also to some extent in the same individual exposed to high environmental stress on different occasions. Such variations are not totally understood. It has been shown that the influence of body size and its relationship to aerobic capacity in tolerance to heat could account for about half of the variability, leaving the remainder to be determined. Changes in hydration and salt balance might be responsible for some of the remaining variability. However, the degree of variability in tolerance to hot environments is poorly understood. Nevertheless, some individuals exhibit poor tolerance to heat and, of this group, some may have hormonal issues that disrupt their ability to control fluids and electrolytes, which increases their susceptibility.